1. Field of the Invention
The present invention relates to an input/output unit which can be used as both of an input unit and an output unit of a control unit such as a computer.
2. Prior Art
In a recent electronic apparatus, a computer is used to control of various machines and detection of data. For example, the computer is used for control of a motor or a solenoid-controlled valve, detection of a rotational speed of a motor, detection of a flow rate of fluid adjusted by a solenoid-controlled valve or detection of temperature data. These types of control are performed by supplying a signal to a motor drive circuit, a solenoid-controlled valve circuit or the like.
Generally, in order to control the various general-purpose machines by means of a computer, the various machines and the computer are connected by cables or the like. An output unit and an input unit are connected between the various machines and the computer.
Control devices such as sensors, switches and the like are provided in the various machines to be controlled. Information from detection devices is inputted through the input unit to the computer. Further, various commands are transmitted from the computer through the output unit to the control devices.
In the prior art method as described above, however, there are problems as follows:
A first problem is that the output unit and the input unit are exclusive units for output and input, respectively, and accordingly two kinds of units are required separately.
A second problem is as follows: For example, when the number of output signals from the computer is larger than the number of input signals to the computer, many output units are required. On the other hand, a plurality of input ports provided in the input unit include useless ports. Thus, the conventional output unit and input unit include uselessports depending on kinds of the control machines.
A third problem concerns shielding for noise. More particularly, various apparatuses often produce noise. The noise produced by the appartuses are transmitted through cables and input units to the computer. The computer sometimes fails to operate in the normal manner due to the noise.
In order to shield the computer from the noise to input signal lines or from output signal lines, a complicated filter circuit adapted to noise is required and is relatively expensive.